The invention relates to a process for the chromatographic determination of ions, particularly anions on a reversed-phase column.
Ever since the arrival of ion chromatography there have been constant improvements to the quantitative analysis of organic and inorganic ions, particularly anions. Due to the poorer column or separation efficiency and the high price, as well as the instability of ion exchange columns, so-called reversed-phase columns have been investigated. In addition, the ions to be determined have been determined by indirect detection methods, such as e.g. indirect identification in the UV-spectral range. However, the chromatograms obtained with reversed-phase columns and indirect identification methods frequently have additional peaks (so-called system peaks) or poorly formed peaks, which make the detection and quantitative determination of the individual ions difficult or even impossible.
The publication by Frank G. P. Mullins (Analyst, May 1987, Vol. 112, pp. 665 to 671) describes an ion chromatographic process for the determination of inorganic anions by an indirect UV-detection method. The column used is dynamically loaded with hexadecyl trimethyl ammonium bromide. Although the chromatogram has no system peaks, not all inorganic anions can be determined, (as e.g. defined by DIN or EPA standards). Thus, it is not possible to detect fluoride and sulphate ions. In LC-GC, 1987, Vol. 4, No. 10, p. 1026 ff, B. E. Andrew describes the use of quaternary ammonium compounds for the ion chromatography of anions. Tetraalkyl ammonium hydroxides are used as ammonium compounds and the straight-chain alkyl radical can contain 1 to 5 C-atoms. In the ion chromatographic determination according to Andrew, system peaks occur in the chromatogram and it is not possible to analyze the anions in one chromatographic run. Andrew also pointed out that a variation in the chain length of the alkyl chains led to no advantages regarding the performance of the process.